Past and future sea-level change from the surface mass balance of glaciers

We present estimates of sea-level change caused by the global surface mass balance of glaciers, based on the reconstruction and projection of the surface mass balance of all the individual glaciers of the world, excluding the ice sheets in Greenland and Antarctica. The model is validated using a leave-one-glacier-out cross-validation scheme against 3997 observed surface mass balances of 255 glaciers, and against 756 geodetically observed, temporally integrated volume and surface area changes of 341 glaciers. When forced with observed monthly precipitation and temperature data, the glaciers of the world are reconstructed to have lost mass corresponding to 114 +/- 5 mm sea-level equivalent (SLE) between 1902 and 2009. Using projected temperature and precipitation anomalies from 15 coupled general circulation models from the Coupled Model Intercomparison Project phase 5 (CMIP5) ensemble, they are projected to lose an additional 148 +/- 35 mm SLE (scenario RCP26), 166 +/- 42 mm SLE (scenario RCP45), 175 +/- 40 mm SLE (scenario RCP60), or 217 +/- 47 mm SLE (scenario RCP85) during the 21st century. Based on the extended RCP scenarios, glaciers are projected to approach a new equilibrium towards the end of the 23rd century, after having lost either 248 +/- 66 mm SLE (scenario RCP26), 313 +/- 50 mm SLE (scenario RCP45), or 424 +/- 46 mm SLE (scenario RCP85). Up until approximately 2100, ensemble uncertainty within each scenario is the biggest source of uncertainty for the future glacier mass loss; after that, the difference between the scenarios takes over as the biggest source of uncertainty. Ice mass loss rates are projected to peak 2040 similar to 2050 (RCP26), 2050 similar to 2060 (RCP45), 2070 similar to 2090 (RCP60), or 2070 similar to 2100 (RCP85).